1. Field of the Invention
The invention relates to a machining apparatus for machining an end face of a tapered roller, and a grinding wheel body used in the machining apparatus.
2. Description of Related Art
In a tapered roller bearing, a large end face (a bottom surface of a cone) of a tapered roller comes in sliding contact with a collar portion provided at an end portion of an inner ring in an axial direction, and hence the large end face is subjected to finishing for reducing a frictional resistance. An example of an apparatus for machining the large end face includes a machining apparatus disclosed in Japanese Patent Application Publication No. 2005-297181 (JP 2005-297181 A).
In addition, the machining apparatus for machining the large end face of the tapered roller includes a machining apparatus shown in FIG. 9. The overall shape of the machining apparatus is substantially circular, and the machining apparatus includes a grinding wheel 91 in a shape obtained by removing a part of the circle (also referred to as a C-shape or a horseshoe shape). The grinding wheel 91 has a C-shaped base metal portion 92 made of steel and a grinding wheel portion 93 fixed along the inner periphery of the base metal portion 92.
In the machining apparatus, a tapered roller 95 is successively loaded from a part of an area A in which the grinding wheel 91 is absent (the right side in the area A in the case of FIG. 9), and a large end face 96 is brought into sliding contact with the grinding wheel portion 93 while the loaded tapered roller 95 is caused to revolve about a vertical line P with the large end face 96 directed outward in a radial direction, whereby it becomes possible to machine the large end face 96. Note that the revolving tapered roller 95 also rotates on its roller axis. The tapered roller 95 makes substantially one revolution along the inner peripheral surface of the grinding wheel 91, and the machining of the large end face 96 is thereby completed, and the tapered roller 95 of which the machining is ended is successively ejected from the other part of the area A (the left side in the area A in the case of FIG. 9).
The grinding wheel 91 is installed so as to be detachable from an apparatus main body 94 of the machining apparatus for maintenance management. For example, the base metal portion 92 of the grinding wheel 91 is fixed to the apparatus main body 94 using a jig including a bolt or the like that is not shown, and the grinding wheel 91 can replaced by detaching the bolt.
When the machining of the large end face 96 of the tapered roller 95 is continuously performed by using the machining apparatus that includes the grinding wheel 91 shown in FIG. 9, degradation such as that abrasive grains of the grinding wheel portion 93 are flattened or become blunt or that the grinding wheel portion 93 (grinding wheel surface) is worn and its radius (inner diameter) is increased occurs. In this case, the large end face 96 cannot obtain a desired shape or machining accuracy is reduced.
In addition, in the case where the machining of the large end face 96 is performed by using the above machining apparatus, in particular, in an area on a side of the end of the machining (the left side in the case of FIG. 9), the machining accuracy of the large end face 96 is significantly influenced. To cope with this, as described above, in the case where the grinding wheel portion 93 is degraded and the machining accuracy of the large end face 96 is reduced, the maintenance management is required particularly in the part of the grinding wheel 91 on the side of the end of the machining. In the related art shown in FIG. 9, the grinding wheel portion 93 is fixed to the base metal portion 92, and hence, in the case where, e.g., the replacement is performed as the maintenance management, it is not possible to replace only the part of the grinding wheel portion 93 on the side of the end of the machining, and it is necessary to replace the entire grinding wheel 91 including the grinding wheel portion 93 and the base metal portion 92.